ERROR in TypeError: Cannot read property 'flags' of undefined

Question

I have a problem when I try to run ng serve on a recently created Angular project. The version I\'m using is 9.1.4, this error does not occur on a project with

Answer 1

9.1.6 just released, should fix that issue

Answer 2

edit

If you use angular 9.1.6 it should be fine now

npm update @angular/cli @angular/core

original post

Something is broken in Angular 9.1.5 - if you run the following it should work:

npm install @angular/core@9.1.4 @angular/animations@9.1.4 @angular/common@9.1.4 @angular/forms@9.1.4 @angular/platform-browser@9.1.4 @angular/router@9.1.4 @angular/platform-browser-dynamic@9.1.4 @angular/compiler@9.1.4 @angular/compiler-cli@9.1.4 @angular/language-service@9.1.4

ng build

Just spent about 4-5 hours trying to fix it myself...

The issue seems to stem from using Angular CLI 9.1.4 with Angular 9.1.5 (most likely the compiler

You'll see the issue when you do

ng --version

if you get:

Angular CLI: 9.1.4
Node: 12.16.3
OS: win32 x64

Angular: 9.1.5
... animations, cli, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

Then you will need to follow the npm installs i listed above

Answer 3

@Matt's answer worked for me as well for ng serve, but needed additional steps. First do these steps "Quoting the steps from his answer":

1. First check ng --version. Go to next step if you get:

Angular CLI: 9.1.4
Node: 12.16.3
OS: win32 x64

Angular: 9.1.5
... animations, cli, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

2. Force reinstall the angular packages with 9.1.4 as the version using:

npm install @angular/core@9.1.4 @angular/animations@9.1.4 @angular/common@9.1.4 @angular/forms@9.1.4 @angular/platform-browser@9.1.4 @angular/router@9.1.4 @angular/platform-browser-dynamic@9.1.4 @angular/compiler@9.1.4 @angular/compiler-cli@9.1.4 @angular/language-service@9.1.4

Couple of more steps for more ng serve to finally work.

1. Next error I got was about tslib: An unhandled exception occurred: Cannot find module 'tslib' For this I installed the tslib package manually using npm.
2. Next error I got was You seem to not be depending on "@angular/core" and/or "rxjs". This is an error.. For this I referred "You seem to not be depending on "@angular/core"." and voila! ng serve worked!

Answer 4

try this solution :

npm install @angular/core@9.1.4 @angular/animations@9.1.4 @angular/common@9.1.4 @angular/forms@9.1.4 @angular/platform-browser@9.1.4 @angular/router@9.1.4 @angular/platform-browser-dynamic@9.1.4 @angular/compiler@9.1.4 @angular/compiler-cli@9.1.4 @angular/language-service@9.1.4

npm install

ng serve